This invention relates to a method and apparatus for metering the delivery of liquids, particularly in small quantities and at high rates. The invention is particularly applicable to the metering of fuel to an internal combustion engine, however it will be readily appreciated that there are other applications for the invention. Examples of other applications are the metering of additives or reaction agents in industrial processes, such as chemical processes. However, for convenience, the invention will now be specifically described and illustrated with reference to its application to metering fuel to an internal combustion engine.
The advantages of metering fuel to an engine by an injection system as compared with a carburation system are well recognised. Because of the improved control over the quantity of fuel delivered to the engine achieved by fuel injection systems, a lower specific fuel consumption is achieved together with an increased power output. Also fuel injection systems result in a lower pollution level in the exhaust gases from the engine and improved starting and acceleration characteristics of the engine.
Although there are known a number of effective fuel injection systems, the carburettor is still the preferred means of metering the fuel to the engine as it is cheaper to manufacture and less expensive to maintain, partly because it is primarily a low pressure device. The high pressure encountered in fuel injection systems require high precision in the sizing and surface finish of many components, particularly in fuel pumps and metering devices, together with high precision and quality in seals between moving parts. In known fuel injection systems the injection is usually achieved by mechanical mechanisms, such as pistons moving in cylinders, and in view of the high pressure required to inject the fuel the forces involved are correspondingly high, and thus absorb significant energy, and require materials and surface treatments to reduce wear.
In view of the relatively high costs of manufacture of known fuel injection systems they are currently not used on the more popular makes of motor vehicles in the high volume low cost category. However, in view of the increasing requirements for low pollution levels in exhaust gases, it would be desirable to incorporate fuel injections systems on all motor vehicles, provided this could be done at a reasonable cost.
In U.S. Pat. No. 3,556,682 granted to Sakamoto et al there is disclosed an apparatus for transferring liquids which operates according to the principle of alternate displacement of liquid in a closed vessel. This apparatus operates on the basic concept of having a closed chamber of a fixed volume with inlet and outlet valves at the lower end for the liquid to be transferred, and inlet and outlet valves, at the upper end for the driving liquid. The transfer liquid is pumped in through the bottom inlet valve whilst the top outlet valve is open, so that the driving liquid in the chamber may be displaced by the incoming transfer liquid. When the chamber has been filled to its total capacity, or to a predetermined level, with the transfer liquid, the transfer liquid inlet valve and the driving liquid outlet valve are closed, and the transfer liquid outlet valve and driving liquid inlet ports are open. Driving liquid is them pumped into the top of the chamber through the driving liquid inlet valve to displace the transfer liquid in the chamber through the transfer liquid outlet valve at the bottom of the chamber.
In the description of the apparatus disclosed in the Sakamoto et al specification with reference to FIG. 1 thereof, no information is given as to how the operation of the valves is controlled. However it does appear that in each cycle the chamber is completely filled with transfer liquid, and then that complete quantity of transfer liquid is discharged by the driving liquid. Accordingly on each cycle the same quantity of liquid is transferred and there is no way in which the quantity of liquid transferred in each cycle can be varied.
In the various other embodiments of the apparatus as described in that prior specification with reference to FIGS. 2 to 16, the same general cylinder and valve arrangement is used as discussed above in connection with FIG. 1. However, there is provided in the cylinder a float which moves up and down in the cylinder on the surface of the transfer liquid and acts in the manner of a floating piston between the transfer and driving liquids. The float carries a peripheral band of magnetic material and two magnetic sensors are located externally of the cylinder, and spaced apart a distance determined by the quantity of liquid to be transferred during each cycle.
As the float reaches the levels of the respective magnetic sensors, the magnetic band on the periphery of the float activates the sensor so that a signal is passed to the mechanism controlling the valves to carry out the appropriate opening and closing of valves.
There is no suggestion in the specification that the quantity of transfer liquid delivered during each cycle can be regulated as the magnetic sensors have a fixed position relative to the chamber. This is not surprising as the apparatus disclosed in the specification is basically a pumping apparatus for the transfer of liquid from one location to another, and is not intended to be a measuring or metering apparatus whereby precisely measured quantities of liquid are delivered during each cycle. The magnetic sensors which detect the position of the float in the chamber are not for the purposes of determining the quantity of liquid transfer of each cycle, but are purely for the purposes of having a means of automatic operation of the valves so that the apparatus can be operated continuously for a large number of cycles without risk of malfunction.
As referred to in the specification, this type of apparatus is primarily used for the pumping of high viscosity liquids, such as slurries of coal or mineral materials, where more conventional pumps cannot be employed.
It is evident that the apparatus disclosed in the Sakamoto et al specification is not intended to be used for the delivery of an accurately measured quantity of liquid each cycle, and there is no indication as to how the quantity of liquid delivered each cycle can be varied in accordance with external demand parameters. It is further evident that as it is intended for the driving fluid to be recycled, there should be no intermixing of the driving liquid and the transfer liquid. Thus, as stated in the specification, the density of the transfer liquid must be substantially greater than that of the driving liquid. Finally it is also evident that the cycle time of the apparatus disclosed in the Sakamoto specification is relatively long, and it could not operate on a cycle time of one second as less as is required in many applications of liquid metering equipment.
There has been proposed in U.S. Pat. No. 3,698,368 a fuel injection system for two-cycle engines, however it is not known that this system has been proved commercially successful. In several embodiments of this system described in the United States patent specification a rigid piston is employed and thus these embodiments exhibit the general disadvantages discussed hereinbefore in connection with known fuel injection systems.
In one embodiment a diaphragm pump is used and the suction stroke of the pump varied in order to meter the quantity of fuel delivered. It is believed that the inherent high flexibility of a diaphragm would operate against the attainment of accurate metering of fuel.
In French Patent No. 521309 there is disclosed a carburettor pump for two-stroke engines wherein there is delivered a charge of air under pressure to the working cylinder of the engine, and a measured quantity of fuel is picked up by the charge of air as the air is travelling to the working cylinder of the engine. Accordingly, the fuel is not truly injected but the fuel is just moved to a position within the stream of air, and that stream of air basically atomizes and/or vaporises the fuel so that it becomes entrained in the stream of air.
As the disclosure in this specification is not related to a true injector system, the fuel will only be subjected to relatively low pressures, particularly as the fuel is not required at any stage to be injected into the working cylinder of the engine against the pressures in the working cylinder. Accordingly, the sealing problems and the fine tolerances which are encountered in normal fuel injection systems would not be present in the system disclosed in this specification.
In addition, the chamber in which the quantity of fuel is measured is required to move into and out of the passage of the air once each revolution of the engine. Accordingly there will be considerable wear over a period of time of the working parts which must lead to fuel leakage and consequently loss of accuracy in the quantity of fuel delivered.
Accordingly, it is seen that the carburettor pump, as disclosed in this French patent, if applied to a high pressure true fuel injection system, would have the same problems as the conventional injector system, that is, the high manufacturing costs and wear associated with manufacturing and operating moving parts at relatively high speed and with high rates of wear, further aggravated by the need to maintain effective seals between the moving components against leakage of fuels subjected to high pressures.
French Patent No. 2050728 discloses a true fuel injection metering arrangement wherein the fuel is displaced from a metering chamber by a gas under high pressure that injects the measured quantity of fuel into the working chamber of the engine. Apart from its high pressure operation, in most other regards, the injection system of this prior specification is very similar to that of French Patent No. 521309. It still requires the chamber that effects the metering of the fuel quantity to be moved between a position in which it receives the fuel to a position at which the fuel is discharged from the chamber by high pressure gas.
The difference between the two French constructions is that in one the member carrying the chamber is subjected to a reciprocating movement, whereas, in the other it is subjected to a rotatory movement. The extent of the movement of the member carrying the chamber in French Patent No. 2050728 is relatively small which is desirable from the point of view of reducing wear, however, it is not a continuous rotary motion but a step-wise motion. The chamber member would, during each cycle, rotate through one-quarter of a revolution with stationary periods at each end of the movement. This type of intermittent movement does of course increase the rate of wear between the mating moving surfaces, and hence the maintaining of an effective seal between the two moving components would still be a major problem.
Another problem with the proposed construction in both the French patents is that in each at least some of the seals between the moving component and the stationary component would be in contact with a surfase that is not a smooth continuous surface which would be most detrimental to the effective life of the seals.
It is seen that the construction disclosed in both the French patents uses a chamber formed in a movable member that must go through one cycle of movement for each delivery of fuel. The French constructions therefore basically have the same problems as always exist where it is endeavoured to contain the measured quantity of fuel in a chamber formed in or by a movable member and then effect movement of that member when theh delivery of fuel is required. Thus both of the proposed French constructions have all of the problems associated with the conventional fuel injection system, including manufacturing to close tolerances to obtain required sealing and the wear arising from high speed and high frequency operation.
In view of the relatively high costs of manufacture of known fuel injection systems they are currently not used on the more popular makes of motor vehicles in the high volume low cost category. However, in view of the increasing requirements for low pollution levels in exhaust gases, it would be desirable to incorporate fuel injections systems on all motor vehicles, provided this could be done at a reasonable cost.